DE102016122888A1 - Solid oxide fuel cell, fuel cell stack and process for producing a solid oxide fuel cell - Google Patents

Abstract

The invention relates to a solid oxide fuel cell with a membrane electrode assembly (MEA) having at least the following features: a mechanical support structure of an open-pore metal foam material, an anode layer of the MEA applied to the surface of the metal foam material of the support structure, substantially not penetrating the metal foam material and gas-tightly applied thereto The electrolyte membrane of the MEA made of a solid oxide material, a cathode layer of the MEA.Die invention also relates to a fuel cell stack and a method for producing a solid oxide fuel cell.

Description

The invention relates to a solid oxide fuel cell according to claim 1, a fuel cell stack according to any one of claims 9, 10 and a method for producing a solid oxide fuel cell according to claim 11.

Like batteries, fuel cells serve to directly convert chemical energy into electrical energy. The core of a fuel cell is the membrane electrode assembly or membrane electrode assembly (MEA), which consists of an anode layer, a cathode layer and an electrolyte membrane separating the anode layer from the cathode layer. For generating electricity, the anode layer is supplied with fuel gas, for example hydrogen, while the cathode layer is supplied with oxidizing gas, for example air. This results in an oxidation of fuel gas at the anode layer, wherein the electrons emitted from the fuel gas migrate via an electrically conductive connection from the anode layer to the cathode layer, where they reduce the oxidation gas. The resulting negative oxidation gas ions combine with the positively charged fuel gas ions. If, for example, hydrogen (H ₂ ) is used as the fuel gas and oxygen (O ₂ ) is used as the oxidizing gas, oxygen ions O ^2- in and at the anode layer combine with hydrogen ions H ⁺ to form water molecules H ₂ in the case of a solid oxide fuel cell (SOFC) O. The released energy can be used by switching a load between the anode and the cathode.

Since a single fuel cell provides only a low electrical voltage (typically between 0.1 V and 1 V), it is common to electrically connect many fuel cells in the form of a fuel cell stack (fuel cell stack) so that the voltages of the individual fuel cells of the stack add. In each case, the cathode layer of a fuel cell is connected to the anode layer of the adjacent fuel cell via a bipolar plate. The bipolar plate separates a flow region of the fuel gas from a flow region of the oxidation gas.

In a solid oxide fuel cell, the electrolyte membrane is formed of a solid material, e.g. a ceramic material that is capable of conducting oxygen ions but still acts as an insulator for electrons. Solid oxide fuel cells are considered to be high temperature fuel cells that operate at an operating temperature of, e. 650 ° C to 1000 ° C are operated.

There are also proposals for metal foam-supported solid oxide fuel cells (MFS-SOFC: Metal Foam Supported SOFC), e.g. in the publication "Metal supported SOFC on the gradient permeable metal foam substrate", Advanced Materials Research Vols. 123-125 (2010), pages 1083-1086.

The invention has for its object to improve such MFS SOFC in terms of production and application functionality. Furthermore, an advantageous fuel cell stack is to be specified with such MFS-SOFC.

1. a) eine mechanische Stützstruktur aus einem offenporigen Metallschaummaterial,
2. b) eine auf der Oberfläche des Metallschaummaterials der Stützstruktur aufgebrachte, in das Metallschaummaterial im Wesentlichen nicht eindringende und darauf gasdicht aufgebrachte Anodenschicht der MEA,
3. c) eine Elektrolytmembran der MEA aus einem Festoxidmaterial,
4. d) eine Kathodenschicht der MEA.

This object is achieved according to claim 1 by a solid oxide fuel cell with a membrane electrode assembly (MEA) having at least the following features:

1. a) a mechanical support structure of an open-pore metal foam material,
2. b) an anode layer of the MEA, which is applied to the surface of the metal foam material of the support structure and essentially does not penetrate the metal foam material and is applied in a gas-tight manner thereto;
3. c) an electrolyte membrane of the MEA made of a solid oxide material,
4. d) a cathode layer of the MEA.

The invention has the advantage that the fuel cell according to the invention can be operated at comparatively low operating temperatures, e.g. below 600 ° C. A further advantage is that the solid oxide fuel cell according to the invention is ready for use more quickly, since it can be "booted up" faster. This is possible because in the fuel cell according to the invention scarcely or at least significantly less mechanical stresses occur during start-up, which result from different coefficients of thermal expansion of the adjoining materials, e.g. the metal foam material and the anode layer material. A further advantage is that the fuel cell according to the invention has an improved durability and thus lifetime, in particular an increased number of possible startup and shutdown processes (temperature cycles).

Furthermore, a significantly larger three-phase limit in the region of the layers of the MEA can be realized in the fuel cell according to the invention, which in turn leads to a significantly increased current efficiency and power density compared to conventional fuel cells.

For example, the solid oxide fuel cell may include a fuel gas chamber or may be coupled to a fuel gas chamber. The fuel gas chamber is then in fluid communication with the anode layer of the MEA, such that a fuel gas may be supplied to the anode layer. The solid oxide fuel cell may further be coupled to an air chamber or to an air chamber. The air chamber is then in fluid communication with the cathode layer of the MEA. In this way, the cathode layer, air or other oxygen-containing gas or oxygen can be supplied. The anode layer may in particular be designed such that it does not penetrate into the metal foam material at all.

According to an advantageous development of the invention, it is provided that the solid oxide material of the electrolyte membrane extends into the anode layer in a concentration which reduces toward the support structure. In this way, the interfaces between the anode layer and the electrolyte membrane can be increased (increase in the three-phase boundary), which supports the aforementioned increased current efficiency and power density. The solid oxide material of the electrolyte membrane may extend all the way to the outside of the anode layer, i. to the interface at which the anode layer is adjacent to the mechanical support structure.

According to an advantageous development of the invention, it is provided that the solid oxide material of the electrolyte membrane extends into the cathode layer of the MEA with a concentration which decreases further away from the support structure. In this way, the interface between the electrolyte membrane and the cathode layer can be increased (increase in the three-phase boundary), which supports the mentioned increased current efficiency and power density. The solid oxide material of the electrolyte membrane may extend all the way to the outside of the cathode layer, i. to the interface at which the cathode layer is adjacent to another mechanical support structure or connected to the air chamber. The enlargement of the interface on the cathode layer side can be further assisted by a porous layer structure of the MEA.

According to an advantageous embodiment of the invention, it is provided that a fuel gas chamber of the solid oxide fuel cell is at least partially formed by the mechanical support structure of the open-cell metal foam material or is connected by this support structure with the anode layer. This has the advantage that the fuel cell can be kept compact in structure, since the metal foam material of the mechanical support structure can at least partially serve as a fuel gas chamber at the same time.

According to an advantageous development of the invention it is provided that on the outside of the cathode layer, a further mechanical support structure of an open-cell metal foam material is arranged. In this way, a mechanically particularly robust fuel cell is realized, which can withstand high external loads, in particular vibration loads. The further mechanical support structure of the open-cell foam material may form at least a part of the air chamber. This also supports the compact design of the fuel cell.

According to an advantageous development of the invention, it is provided that the MEA is formed without sintered material regions. In this way, an MEA with high material homogeneity can be realized, which is largely insensitive to mechanical vibrations and has a highly efficient electrical functionality. The MEA may e.g. be prepared by vapor deposition, as will be explained in more detail below.

According to an advantageous development of the invention, it is provided that the MEA runs along lateral boundary surfaces of the mechanical support structure. In this way, the fuel cell can be made simpler and more robust since the joints or interfaces to be sealed can be reduced, e.g. by 33%. Accordingly, in the fuel cell according to the invention, leakage problems and associated functional deteriorations are less likely to occur.

The solid oxide fuel cell may have in plan view a total round cross-sectional shape or at least a cross-sectional shape with rounded corners. In this way, the mechanical robustness and durability of the fuel cell is further improved.

The metal foam material may e.g. to be a nickel foam. The anode layer may e.g. by yttrium, zirconium, nickel or a mixture thereof, e.g. through YSZ. It may also be an alloy with one of the aforementioned metals, e.g. Nickel-aluminum. Yttrium and / or zircon can be used to form the electrolyte membrane. For the cathode layer, e.g. Platinum and / or LSM are used.

The aforementioned object is further achieved by a fuel cell stack having a stacked arrangement of a plurality of solid oxide fuel cells of the type described above. This also makes it possible to realize the advantages explained above.

The object mentioned at the outset is furthermore achieved by a fuel cell stack which has a stacked arrangement of several Has solid oxide fuel cells, for example, solid oxide fuel cells of the type described above or other, known type, wherein adjacent fuel cells with their respective anode side of the MEA or with their respective cathode side of the MEA are arranged facing each other. In this way, the fuel cell stack is arranged with the individual fuel cells in a kind of "Janus principle", so that immediately adjacent fuel cells are to be electrically connected in parallel. This structure of the fuel cell stack allows a simplified execution of the individual fuel cells, since gas supply structures and gas discharge structures and the required metal foam support structures can be reduced. Also, the aforementioned bipolar plate can be omitted. In addition, this significantly simplifies the production, gas supply and stack assembly compared to conventional fuel cell stacks.

1. a) Bereitstellen der mechanischen Stützstruktur aus dem offenporigen Metallschaummaterial,
2. b) Erzeugen einer in das Metallschaummaterial im Wesentlichen nicht eindringenden und darauf gasdicht aufgebrachten Anodenschicht einer MEA der Festoxidbrennstoffzelle,
3. c) Fertigstellen der MEA mit einer Elektrolytmembran und einer Kathodenschicht.

The above-mentioned object is further achieved by a method for producing a solid oxide fuel cell, which has a mechanical supporting structure made of an open-pore metal foam material, with the following steps:

1. a) providing the mechanical support structure of the open-pore metal foam material,
2. b) producing an anode layer of an MEA of the solid oxide fuel cell which does not penetrate the metal foam material in a gas-tight manner and is applied thereon in a gas-tight manner;
3. c) Completing the MEA with an electrolyte membrane and a cathode layer.

This also makes it possible to realize the advantages explained above. In this way, in particular a solid oxide fuel cell of the type described above can be produced.

According to an advantageous development of the invention, it is provided that the mechanical support structure is infiltrated before the application of the anode layer with a curable infiltration material filling the pores of the open-pore metal foam material of the support structure. This has the advantage that the open-pore metal foam material can be at least temporarily closed by means of the infiltration material, i. the pores are filled, so that it can be prevented in this way that the deposited material of the anode layer penetrates into the metal foam material. The surface of the mechanical support structure filled with the infiltrating material to be coated with the anode layer may be e.g. be smoothed before applying the anode layer, e.g. by grinding and / or polishing. The grinding and / or polishing takes place so far that the metal foam is reached. In this way it can be particularly effectively prevented that material of the MEA, in particular the electrolyte membrane, penetrates into the metal foam material of the support structure. The infiltrating material may e.g. a polymer that is curable via a hardener.

According to an advantageous development of the invention, it is provided that the infiltration material is removed from the support structure after completion of the MEA or at least the anode layer. The removal of the infiltrating material may e.g. done by thermal and / or chemical influence. Thus, e.g. a relatively low melting point infiltrating material can be converted to the liquid and / or gaseous state by heating, so that it can be removed from the support structure in this way. The chemical removal of the infiltrating material may e.g. by introducing a solvent, e.g. Acetone, to be performed. In this way, the infiltration material is dissolved and removed with the solvent from the support structure.

According to an advantageous development of the invention, it is provided that the anode layer, the electrolyte membrane and / or the cathode layer of the MEA are produced by means of vapor deposition. In this way, the MEA can be produced with the mentioned three layers in a simple, fast and cost-effective manner. Another advantage is that by means of vapor deposition, e.g. in a Koverdampfungsprozess, the aforementioned transitions of the solid oxide material of the electrolyte membrane in the anode layer and / or in the cathode layer can be realized. This can e.g. in that, in the vapor deposition process, first the anode layer material is vaporized at high concentration, then the solid oxide material is added to the electrolyte membrane with increasing concentration, whereby the deposition of the anode layer material is reduced. Finally, at a later time, the deposition rate of the solid oxide material is reduced, while at the same time the deposition rate of the cathode layer material is increased.

For the vapor deposition known processes of chemical vapor deposition (CVD - chemical vapor deposition) or physical vapor deposition (PVD - physical vapor deposition) can be used. The cathode layer may alternatively be replaced by other methods, e.g. thermal spraying, applied.

According to an advantageous embodiment of the invention it is provided that the mechanical support structure is coated on opposite outer surface sides, each with a separate anode layer. In this way, this mechanical support structure a common Support structure for two adjacent fuel cell of a fuel cell stack, which is realized in the aforementioned Janus arrangement form. In this way, such a fuel cell stack can be produced in a particularly simple and cost-effective manner.

• 1 eine Festoxidbrennstoffzelle in Schnittdarstellung und
• 2 eine Ausschnittsvergrößerung aus 1 sowie ein Diagramm der Materialkonzentrationen in der MEA und
• 3 einen Brennstoffzellenstapel in Schnittdarstellung und
• 4 eine weitere Ausführungsform einer Festoxidbrennstoffzelle in Schnittdarstellung und
• 5 eine weitere Ausführungsform eines Brennstoffzellenstapels in Schnittdarstellung.

The invention will be explained in more detail by means of embodiments using drawings. Show it

• 1 a solid oxide fuel cell in a sectional view and
• 2 an excerpt from 1 as well as a diagram of the material concentrations in the MEA and
• 3 a fuel cell stack in section and
• 4 a further embodiment of a solid oxide fuel cell in a sectional view and
• 5 a further embodiment of a fuel cell stack in a sectional view.

In the figures, like reference numerals are used for corresponding elements.

The in the 1 illustrated solid oxide fuel cell 1 has an MEA 5 on. Above the MEA 5 , on an anode layer 50 the MEA 5 , is a mechanical support structure 3 made of open-pore metal foam material. On the opposite side of the MEA, on a cathode layer 52 , is another mechanical support structure 8th made of open-pore metal foam material. The support structure 3 is circumferentially by a frame 4 edged. The further support structure 8th is circumferentially by another frame 6 edged. The MEA 5 extends through the frame 4 . 6 to an outside of the fuel cell 1 , In this way, an electrical contacting of the MEA 5 on the outside of the fuel cell 1 respectively.

The support structure 3 as well as the support structure 3 comprehensive framework 4 is at the top of the fuel cell 1 through an upper cover plate 2 covered. The further support structure 8th and the frame surrounding the further support structure 6 is at the bottom of the fuel cell 1 through a lower cover plate 7 covered. The fuel cell 1 can supply lines and discharge lines 9 . 10 . 11 . 12 for the fuel gas and an oxygen-containing gas. For example, the fuel gas through the supply line 9 be fed and through the discharge line 10 excess fuel gas and the water formed in the reaction are removed. Through the feed line 11 For example, air can be supplied and via the discharge line 12 the spent air is discharged.

The 2 shows in the left part of the figure an enlarged section of the MEA 5 with a partial section of the support structure arranged above 3 , The right part of the figure shows the respective concentration p of the anode layer material 53 , the solid oxide material 54 the electrolyte membrane and the cathode layer material 55 over a spatial coordinate x passing through the MEA. Visible is that in the middle part of the MEA 5 where the electrolyte membrane 51 is formed, only solid oxide material 54 is available. In the upper edge area, where the anode layer 50 is formed, is a transition between the solid oxide material 54 and the anode layer material 53 available. In the lower area, where the cathode layer 52 is formed, is a transition between the solid oxide material 54 and the cathode layer material 55 available. This can be produced, for example, by vapor deposition in a simple manner.

The 3 shows a fuel cell stack 100 Derived from solid oxide fuel cells based on the 1 explained type is constructed, wherein the individual fuel cells are arranged such that adjacent fuel cells with their respective anode side of the MEA or with their respective cathode side of the MEA are arranged facing each other, as by the in 3 reproduced reference numerals. Accordingly, the entire structure simplifies, since in adjacent fuel cells not twice each support structure 3 or 8th must be present, but only required once. Further, it is sufficient if an upper cover plate 2 for the entire fuel cell stack 100 is present, and accordingly only a lower cover plate 7 ,

The supply lines and discharge lines 9 . 10 . 11 . 12 can at the in 3 shown fuel cell stack eg laterally through the frame 4 . 6 be guided. It may, for example, the supply line 9 from the left through the frame 4 be introduced and the discharge line 10 right through the frame 4 be led out. The feed line 11 can from the left through the frame 6 be introduced and right through the frame 6 the discharge line 12 be led out.

According to the fuel cell 1 and the fuel cell stack according to 3 is at the interfaces between the MEA 5 and the respective frame 4 . 6 one seal required. This effort for the required seals can by the design of the fuel cell according to 4 be reduced. It can be seen that the MEA 5 at the edge region of the support structure 3 ie along a lateral interface of this support structure 3 , runs upward and then laterally (horizontally) along the frame 4 and the upper cover plate 2 is guided. In this way can be a separate frame 6 for the further support structure 8th eliminated, leaving only a single continuous frame 4 is required. This can reduce the amount of connections to be sealed by 33%.

The 5 shows a fuel cell stack 100 according to fuel cell according to 4 in the same manner as the fuel cell stack according to 3 is formed, ie with each other to be facing anode sides or cathode sides of the adjacent fuel cells (Janus principle). In this way, the basis of the 3 already explained advantages with the advantages according to 4 can be advantageously combined, ie it is compared to the embodiment of 3 in turn less seals required. The method for producing a fuel cell of the kind explained above starts with the infiltration of the open-cell metal foam by an infiltration material. This infiltration material may be, for example, a material having a melting temperature well below 600 ° C or a chemically soluble material. The solvent should attack neither nickel nor yttrium stabilized zirconia (YSZ) or the cathode layer, which may consist of common SOFC cathode materials. The surface of the metal foam infiltrated with the infiltration material is now prepared by grinding and polishing for a coating, degreased and introduced into the coating system. All common methods for producing the anode layer from the gas phase can be used, for example the physical vapor deposition with magnetron support. The coating process is carried out under an argon-oxygen atmosphere. The composition of the gas mixture is between: 95% argon and 5% oxygen and 50% argon and 50% oxygen. The oxygen content can be varied cyclically between 0% oxygen and the desired percentage to improve the deposition rate. As an additional additive to the gas mixture, krypton may be added to stabilize the coating process. The coating materials used are, for example: nickel, zirconium, yttrium and optionally platinum or other cathode materials. In addition to the use of zirconium and yttrium, YSZ can also be used as a coating material. In this case, an argon atmosphere without oxygen is used for coating. The performance used to evaporate the coating materials is adjusted to evaporate between 5% and 15% yttrium compared to zirconia.

The coating process is also divided into three phases. In the first phase, in addition to yttrium and zirconium, nickel is also evaporated and applied to the substrate. The nickel content is between 25% and 75% in the resulting layer. The nickel content is lowered in discrete steps or continuously until nickel is no longer added. This preferably happens in the first 2.5 μm of the layer. In the second process phase, only yttrium and zirconium are separated. The layer thickness produced here can be up to 500 microns, preferably, the layer thickness is between 5 microns and 30 microns here. If conventional methods for cathode layer production are used, the coating process ends here. In the preferred process, platinum is vaporized in the third phase. In this case, the platinum content in discrete steps or continuously increased to the desired layer composition with a platinum content between 25% and 75%.

Both the cathode and the anode may be made porous to increase the three-phase boundary. The process pressure during the coating (normally between 0.2 Pa and 1.0 Pa) is significantly increased.

Following the coating and eventual manufacture of the cathode layer, the infiltrate is chemically or thermally liquefied and removed from the metal foam. The metal foam can be integrated into a corresponding frame structure before the start of the process.

The structure of the fuel cell is made of a metal foam in addition to the upper and lower cover plate, preferably other materials possibly nickel, and the applied by the method and on one side connected to the metal foam MEA. This MEA consists of three different layers. Starting from firmly attached metal foam, a mixed layer of anode material follows, in this case nickel and YSZ. The proportions in this layer can vary on the surface in the range of 25% to 75% nickel. The layer typically, but not necessarily, has a gradual buildup with decreasing nickel content. The layer thickness is typically less than 2.5 microns, but may also be thicker. This layer is followed by an electrolyte layer consisting of YSZ. On this a mixed layer of cathode material, here platinum - other materials possible, and YSZ applied. Again, the platinum shares vary between 5% and 75%. The third layer typically has a gradual structure. On the cathode side, the electrical connection is realized by a further metal foam, this can be connected by joining methods such as soldering to the cell or just be hung up. This metal foam is enclosed by a frame. The entire cell is sealed against leaks with seals of various types. The gas supply takes place e.g. through holes in the frame.

Claims (16)

Solid oxide fuel cell (1) with a membrane electrode assembly (MEA) (5) having at least the following features: a) a mechanical support structure (3) made of an open-cell metal foam material, b) an anode layer (50) of the MEA (5), which is applied to the surface of the metal foam material of the support structure (3) and is not penetrated into the metal foam material and is applied gas-tight thereon; c) an electrolyte membrane (51) of the MEA (5) made of a solid oxide material (54), d) a cathode layer (52) of the MEA (5). Solid oxide fuel cell according to the preceding claim, characterized in that the solid oxide material (54) of the electrolyte membrane (51) extends into the anode layer (50) in a concentration which reduces the support structure (3). A solid oxide fuel cell according to any one of the preceding claims, characterized in that the solid oxide material (54) of the electrolyte membrane (51) extends into the cathode layer (52) of the MEA (5) at a concentration decreasing away from the support structure (3). Solid oxide fuel cell according to one of the preceding claims, characterized in that a fuel gas chamber of the solid oxide fuel cell (1) is at least partially formed by the mechanical support structure (3) of the open-cell metal foam material or by this support structure (3) with the anode layer (50). Solid oxide fuel cell according to one of the preceding claims, characterized in that on the outside of the cathode layer (52), a further mechanical support structure (8) is arranged made of an open-cell metal foam material. Solid oxide fuel cell according to one of the preceding claims, characterized in that the MEA (5) is formed without sintered material regions. Solid oxide fuel cell according to one of the preceding claims, characterized in that the anode layer (50) and / or the cathode layer (52) is formed porous. Solid oxide fuel cell according to one of the preceding claims, characterized in that the MEA (5) runs along lateral boundary surfaces of the mechanical support structure (3). A fuel cell stack, characterized in that the fuel cell stack (100) comprises a stacked arrangement of a plurality of solid oxide fuel cells (1) according to one of the preceding claims. A fuel cell stack, characterized in that the fuel cell stack (100) comprises a stacked arrangement of a plurality of solid oxide fuel cells (1), wherein adjacent fuel cells (1) with their respective anode side of the MEA (5) or with their respective cathode side of the MEA (5) are arranged facing each other , Method for producing a solid oxide fuel cell (1), which has a mechanical supporting structure (3) made of an open-pore metal foam material, with the following steps: a) providing the mechanical support structure (3) from the open-cell metal foam material, b) producing an anode layer of an MEA (5) of the solid oxide fuel cell (1) which does not penetrate substantially into the metal foam material and is applied thereon in a gas-tight manner; c) completing the MEA (5) with an electrolyte membrane (51) and a cathode layer (52). Method according to the preceding claim, characterized in that before applying the anode layer (50), the mechanical support structure (3) is infiltrated with a curable infiltration material filling the pores of the open-pore metal foam material of the support structure (3). Method according to the preceding claim, characterized in that the infiltrating material is removed from the support structure (3) after completion of the MEA (5) or at least the anode layer (50). Method according to one of Claims 11 to 13 , characterized in that the anode layer (50), the electrolyte membrane (51) and / or the cathode layer (52) of the MEA (5) are produced by means of vapor deposition. Method according to one of Claims 11 to 14 , characterized in that the support structure (3) infiltrated with the infiltration material is smoothed after it has hardened on a surface on which the anode layer (50) is to be applied. Method according to one of Claims 11 to 15 , characterized in that the mechanical support structure (3) is coated on opposite outer surface sides, each with a separate anode layer (50).

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